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Biochemistry Exam 3 > Chapter 30: Amino Acid Degradation and the Urea Cycle > Flashcards

Chapter 30: Amino Acid Degradation and the Urea Cycle Flashcards

1
Q

What is a ketogenic amino acid?

A

Amino acid carbon skeleton converted to acetyl CoA or acetoacetate

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2
Q

What is a glucogenic amino acid?

A
  • Carbon skeletons converted to pyruvate, alpha-ketoglutarate, succinyl-CoA, fumarate or oxaloacetate
  • Amino acids finally converted to glucose through gluconeogenesis
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3
Q

Amino acids are first used to build new _____. Those not needed for that are catabolized to make use of their _____.

A
  • New proteins
  • Make use of their nitrogen and carbon skeletons
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4
Q

Amino acid degradation primarily occurs in the _____.

A

Liver

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5
Q

First step is often removal of the alpha-amino group to generate _____.

A

Ammonia

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6
Q

After generation of ammonia, the carbon chains are altered for entry into _____.

A

Central pathways of carbon metabolism

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7
Q

Amino acids are made of _____ and _____.

A

Amine group and carboxylic group

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8
Q

What are the 3 key reactions of disposal of amino acids nitrogen?

A
  1. Transamination reactions
  2. Deamination reactions
  3. Glutamine Synthesis
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9
Q

The exchange of the NH2 group with =O group on another molecule is considered to be…

A

Transamination

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10
Q

The first key reaction of disposal of amino groups results in the following reaction:

A

Amino acid + Keto acid –> Keto acid + Amino acid

  • Transamination
  • One becomes the other
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11
Q

What catalyzes the transfer of the alpha-amino group of aspartate to alpha-ketoglutarate?

A

Aspartate transaminase

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12
Q

There are only a few keto acid acceptors. What is the most used?

A

Alpha-ketoglutarate

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13
Q

The second key reaction of disposal of amino groups has two parts:

A

Deamination

  • Oxidative deamination - aerobic conditions
    • Catalyzed by glutamate dehydrogenase
    • Important in liver where it releases ammonia for urea synthesis
  • Hydrolytic deamination
    • Catalyzed by glutaminase and asparaginase
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14
Q

The third key reaction of disposal amino groups:

A

Glutamine Synthetase

NH3 –> Glutamate –> Glutamine

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15
Q

Used as a carrier of ammonia in most tissue

A

Glutamine

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16
Q

Used as a carrier in muscles

A

Alanine

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17
Q

What is the 1st step in amino acid degradation?

A

Nitrogen removal

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18
Q

Some amino acids can be _____ deaminated.

A

Directly

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19
Q

Removal of ammonium from most amino acids involves two steps:

A
  1. Aminotransferases (transaminases) transfer amino groups from an amino acid to alpha-ketoglutarate to generate glutamate
  2. Glutamate dehydrogenase, a mitochondrial enzyme, releases NH4+ in the oxidative deamination of glutamate
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20
Q

Peripheral tissues transport nitrogen to the _____.

A

Liver

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21
Q

Nitrogen can also be transported as _____ formed from glutamate by glutamine synthetase

A

Glutamine

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22
Q

Ammonia is toxic and needs…

A

To be excreted

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23
Q

What happens to excess ammonia?

A

Urea Cycle

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24
Q

What three molecules come into the urea cycle?

A

Ammonia and CO2 and Aspartate

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25
Q

Functions as detoxification of ammonia (prevents hyperammonemia)

A

Urea Cycle

26
Q

Overall Urea Cycle occurs in the _____

A

Liver

27
Q

Urea Cycle takes CO2, NH3 and aspartate + the cost of _____ to produce…

A

Cost of 3 ATP

To produce Urea and Fumarate

28
Q

Glutamate Dehydrogenase reaction

A

Glutamate + NADP+ –> alpha-ketoglutarate + NH3 + NADPH

Generation of NH3

29
Q

CPS Reaction:

A

NH3 + HCO3- + 2 ATP is converted to Carbamyl Phosphate by Carbamyl Phosphate Synthetase

30
Q

CPS I (Mitochondria) uses _____ which is important for _____.

A

Uses NH3 which is important for urea cycle

31
Q

CPS II (Cytosol) uses _____ which is important for _____.

A

Uses glutamine which is important for pyrimidine biosynthesis

32
Q

Bicarbonate is activated by _____ to form _____.

A

Activated by ATP to form carbonyl-P

33
Q

Carbonyl-P is converted to _____.

A

Carbamate

34
Q

Carbamate is phosphorylated by _____. Carbamate converts to _____.

A

By ATP

Converted to carbomoyl phosphate

35
Q

Urea Cycle: Carbamoyl P + _____ –> _____ by _____.

A

Ornithine –> Citrulline by Ornithine transcarbamylase

36
Q

Ornithine + Citrulline are considered _____ amino acids.

A
  • Non-standard (not present in proteins)
  • Carry ammonium group from cytosol to mitochondria or vice versa
37
Q

What gets added from the cytosol to citrulline?

A

Aspartate

38
Q

Citrulline + Aspartate –> _____ by _____.

A

Argininosuccinate by Argininosuccinate synthetase

39
Q

Elimination reaction leads to _____ and _____ (cytosol).

A

Arginine and fumarate

40
Q

Argininosuccinate –> _____ by _____.

A

Arginine by Argininosuccinase (cytosol)

41
Q

In the cytosol, arginine is converted to _____ by _____ which is transported into the _____.

A

Converted to Ornithine by Arginase (cytosol), which is transported into the mitochondria

42
Q

Fumarate can be converted into _____ by the _____ and then into _____ by the _____.

A

Can be converted into oxaloacetate by the citric acid cycle and then into glucose by gluconeogenic pathway.

43
Q

The urea cycle is generally controlled by _____

A

Substrate availability

44
Q

The more ammonia, the higher the rate of _____.

A

Urea formation

45
Q

Defects in any of the urea cycle enzymes results in elevated levels of _____ in the blood, which causes nervous system malfunction and can be lethal.

A

NH4+

46
Q

Excessive alcohol consumption causes…

A

Liver cirrhosis

47
Q
  • Defects in catabolism of branched-chain amino acids
  • Inability to degrade branched amino acids
A

Maple Syrup Urine Disease

48
Q

Which amino acids can be directly deaminated to produce NH4+?

    A. Serine and threonine

    B. Proline and valine

    C. Phenylalanine and tryptophan

    D. Glycine and alanine

    E. No amino acids can be directly deaminated
A

Serine and Threonine

49
Q

Tryptophan is degraded to acetacetyl CoA and pyruvate, making it:

A

Both a ketogenic and glucogenic amino acid

50
Q

Phenylketonuria is caused by a defect in:

        A. Phenylalanine reductase

        B. Succinyl CoA synthetase

        C. Citrulline dehydrogenase

        D. Phenylalanine hydroxylase

        E. Tyrosine transaminase
A

Phenylalanine hydroxylase

51
Q

Essential AAs generally..

A

Generally require higher amounts of energy for their synthesis than non-essential amino acids

52
Q

Which serves a catalytic role in the urea cycle?

  A.   Carbamoyl phosphate

  B.   Aspartate

  C.   Ornithine

  D.   Glutamate

  E.    ATP
A

Ornithine

53
Q

People with Maple Syrup Disease accumulate _____________ in their blood.

A. Leucine, isoleucine and valine

B. Homogentistic acid

C. Phenylalanine

D. Alpha-keto acids

E. Urea

A

Alpha-keto acids

54
Q

Tyrosine can be broken down to fumarate and acetoacetate. Tyrosine is:

  A.   Solely a ketogenic amino acid

  B.   Solely a glucogenic amino acid

  C.   Both a ketogenic and a glucogenic amino acid

  D.   Neither a ketogenic nor a glucogenic amino acid

  E.   It is impossible to tell from this information
A

Both a ketogenic and a glucogenic amino acid

55
Q

In mammals, nitrogen present in amino acids:

A

Comes primarily from dietary protein

56
Q

Lysine is degraded through a series of steps to 2 Acetyl CoA + 2 CO2 molecules. Lysine is:

  A.   Solely a ketogenic amino acid

  B.   Solely a glucogenic amino acid

  C.   Both a ketogenic and a glucogenic amino acid

  D.   Neither a ketogenic nor a glucogenic amino acid

  E.   It is impossible to tell from this information
A

Solely a ketogenic amino acid

57
Q

The two nitrogen atoms in urea are derived from __________ and ________.

A

Ammonia and aspartate

58
Q

Nitrogen levels in the blood increase in the early stages of fasting because:

A

Amino acids become a major source for glucose production

59
Q

Carbamoyl phosphate synthetase catalyzes synthesis of carbamoyl phosphate from NH3, ATP and:

    A. Arginine

    B. Bicarbonate

    C. Urea

    D. Malonyl CoA

    E. Citrate
A

Bicarbonate

60
Q

Which two compounds along with 2 ATP are used to make carbamoyl phosphate?

A

Bicarbonate and ammonia

Biochemistry Exam 3 (10 decks)

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